1. Field of the Invention
The invention relates to a semiconductor laser device and a manufacturing method thereof. More particularly, the invention relates to a semiconductor laser device having a chip end facet formed by cleavage, and a manufacturing method thereof.
2. Background Art
III-V compound semiconductor laser devices such as aluminum gallium arsenic (AlGaAs)-based infrared laser devices or indium gallium phosphorus (InGaP)-based red laser devices have been widely used as elements of communication devices or as reading and writing elements of CDs (Compact Discs) or DVDs (Digital Versatile Discs). Recently, blue or ultraviolet semiconductor laser devices having a shorter wavelength have been implemented by using a nitride semiconductor represented by general formula AlxGayIn(1-x-y)N (where 0≦x≦1, 0≦y≦1, and 0≦x+y≦1). Semiconductor laser devices using a nitride semiconductor have been gradually used in practical applications as reading and writing light sources of next generation high-density optical discs such as Blu-ray Disc. Blue laser devices of several tens of milliwatts are currently available on the market. However, higher output has been demanded for an improved recording speed, and 100 mW-level laser devices are coming onto the market.
In a semiconductor laser device, a resonator end facet is generally formed by cleavage. In infrared and red semiconductor laser devices that are formed from a semiconductor material having a Zinc-blende structure, such as AlGaAs-based and GaInP-based semiconductor materials, the semiconductor has a cleavage facet at every 90 degrees and therefore has very high cleavage accuracy. However, since a crystal structure of a nitride semiconductor such as GaN is a hexagonal wurtzite structure, the semiconductor has a (1-100) face as a cleavage facet and an equivalent cleavage facet that is 60 degrees away from the (1-100) face. Therefore, upon cleavage, cracks are formed also in the direction of 60 degrees from the cleavage direction, and it is difficult to form a structurally stable cleavage facet.
In order to solve this problem, Japanese Patent Laid-Open Publication No. 2003-17791 discloses a method for forming a scribe mark like a dashed line on a nitride semiconductor layer by using a diamond needle or the like, and conducting cleavage by breaking by using the scribe mark as a cleavage guide. However, when cleavage guide grooves are formed by scribing or dicing, a nitride semiconductor layer is scratched. Therefore, a lot of defects such as end facet cracks, unevenness, fractures, and chips are generated in the grooves themselves, causing a cleavage facet to be displaced. Moreover, since grooves formed by scribing do not necessarily have a uniform shape, it is difficult to accurately control the cleavage position.
Japanese Patent No. 59-14914 and Japanese Patent Laid-Open Publication No. 11-251265 disclose a method for forming cleavage guide grooves by etching. When cleavage guide grooves are formed by etching, the position and shape of the grooves can be accurately controlled.
However, the inventors found that, in the case of a nitride semiconductor, an intended cleavage facet still cannot be obtained even when the cleavage guide grooves are formed. More specifically, as described above, a nitride semiconductor essentially has a poor cleavage property, and has an equivalent cleavage facet in the direction of 60 degrees from a cleavage facet. Therefore, even when cleavage guide grooves are formed, cleavage does not occur along the grooves, or cleavage starts from a portion other than the end of the groove. Accordingly, an intended cleavage facet cannot be obtained.